"There are different styles of RIS, depending on how much the operator will be accessorizing the weapon. Basic systems that can be installed on weapons such as the previously mentioned AR-15/M16 are usually small rails with holes machined in them that are screwed onto the existing hand guard on the rifle and can cost as little as $25 to $40 USD. More advanced systems allow for numerous accessories to be mounted simultaneously and cost an average minimum of $200 USD and up for a decent quality system."

ITS the HANDGUARD part.

If you are just so blockheaded and would absolutely not accept the fact, then here's more proof.